Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Good spark on the dead cylinder? Have you checked the valves? .006 inch intake and exhaust. If valves and spark is good, then check compression on both cylinders.
Have the valves and the compression been checked?
You have a business card? See if you can slip a business card between the valve stem and the valve tip.
That's about .010 inch. It has to have some clearance, but zero will not work.
I am off to church. Try to check the valves and I will check back.